International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
Effect of Temperature on Scale Formation around the Wellbore and Hole
Cleanup for Reconditioned Drilling Mud
Seteyeobot Ifeanyi1, Oyinkepreye D. Orodu1, Efeoghene Enaworu1 and Olawole Kunle Patrick2
1
Covenant University, Ota, Nigeria.
2
Salford University, Salford M5 4WT, UK.
parameter which influence the mobility ratio such as salt
concerntration in the brine, produced water rate, pressure
drawdown and reservoir temperature were identified through
the model. Results of their study shows that the mobility ratio
of a water flooded reservoir remains constant until water
breakthrough and achieves an increasing local maximum at
10% pore volume injected water as the flow rate of produced
water increases with a significant rise beyond the critical flow
rate observed at mobility ratio of 1.
Haarberg et al3 gave an equilibrium model which is capable of
predicting the formation of CaCO3 scales. They were able to
give a detailed description of the model used in calculating the
effect of pressure on CaCO3 precipitation but variation of
permeabilities of the porous medium caused by this
precipitation was not accounted for in the model.
Production problems caused by mineral scale in oil and gas
production operations is a problem that has been known for
long, barium sulphate scale was identified as the most difficult
scale to control among numerous scaling problems. This is as a
result of the low solubility of barium sulphate in most fluids
and the commensurate low reactiveness of most acids with
barium sulphate scale.
This paper presents a Solution [X] (based on experimental
analysis) for effective wellbore and open hole clean up of a
producing well at different temperatures, especially at offshore
locations where seawater is mostly injected. An analytical
model for the prediction of BaSO4 scale build up rate under an
idealized flow condition as derived by Fadairo et al (2008) was
used for prediction of scale formation. We observe technical
issues that influence the impact of BaSO4 scale deposition on
inflow performance and also identify key parameters that
influence the magnitude of BaSO4 scale deposition. Using this
model as a predictive tool, the effective planning for BaSO4
scale treatment (clean up) using Solution [X] during
production operations is applied.
Abstract
Oil based muds are very complex fluids composed from water,
oil, organophilic clays and various additives. Their very good
filtration and lubricating properties make their use beneficial in
numerous drilling operations.
Formation and deposition of scale in wellbore and porous
media due to extensive use of oil based mud for drilling at
different pressures and temperature is a problem that results in
production decline. A variety of models are presently being
used in the oil industry for predictiong scaling tendency and
scale precipitation inside the wellbore and immediate wellbore
region. Some of the precipitated BaSO4 scale escapes through
the pore spaces to render havoc to flow in the production string.
This research is an experimental study that presents a Solution
[X] (based on experimental analysis) for effective wellbore and
open hole clean up of a producing well drilled with Oil Based
Mud at different temperatures, especially at offshore locations
where seawater is mostly encountered. Results from this study
shows that cleanup using referred Solution [X] at low
temperatures yields high success cleanup rate of BaSO4 scale
precipitation as well as when used at high temperature
regardless of the effect of temperature change on solubility of
BaSO4 scale.
INTRODUCTION
Scale can be described as any crystalline deposit (salt) resulting
from the precipitation of mineral or inorganic compounds
present in water. A typical precipitation of inorganic
compounds may include the reaction of anhydrate (CaCO 3),
1
gypsum (CaSO4.H2O), hemihydrates (CaSO4. 𝐻 2O), barite
2
(BaSO4), celestite (SrSO4), magnesium sulphide (MgSO4),
originating from mixing sea water with brine and rock. It could
also be the precipitation of iron hydroxide gel (Fe(OH) 3)
originating from the acid dissolution and other iron minerals
such as pyrhotite (FeS), pyrite (FeS2), hematite (Fe2O3),
magnetite (Fe3O4) and siderite (FeCO3).
Pitzer K.S1 developed general equation for electrolyte mean
activity coefficient. This equation is based on the theory of
interaction of the ions that are involved in the formation of
scale. The equation accounts for both long and short range
electrostatic interactions between ions and the effects of solvent
types on scales formation tendency.
Fadairo et al2 presents an analytical model based on existing
thermodynamic model for predicting brine mobility,
hydrocarbon mobility and mobility ratio of water flooded
reservoir with possible incidence of scale precipitation and
accumulation. The key operational and reservoir/brine
EXPERIMENTAL ANALYSIS
In developing this solution, the properties of an oil based mud,
a reconditioned oil based mud and the mechanism of
impairment to flow that is caused by deposition of scale both
inside the well bore, behind the casing walls and at the pore
throats is considered to be of importance. Some key factors
considered are;
 Movement/transportation of precipitated salt (scale) to
the region of deposition
 Changes in both temperature and pressure conditions as
oil and water are being produced from the reservoir which
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
will bring about a change in the solubility of solid salt in
the reservoir.
 The volume of the pore spaces where scale are deposited
 The degree of resistance to flow caused by the deposited
scale which is as well governed by the relative
permeability of the fluid phase
Step 6. Disc soaked in Solution [X] for varying time until
complete wash out occurs
Test 1
This clean up test was carried out using freshly built mud
(BLEND A)
Test 2
This clean up test was carried out using back loaded mud
(BLEND B)
Based on the factors above the components for Solution [X]
were ascertained and combined at appropriate ratios under
careful laboratory procedures and supervising.
Test 3
This clean up test was carried out using reconditioned mud
(BLEND C)
Formulation:
Product
Concentration
Density
%
SG
XXX
20.0%
1.1140
CaCl2 Brine
32.0%
1.2120
XXX
10.0%
1.0491
XXX
5.0%
1.1800
Water (Free Water)
32.0%
1.0000
Corrosion Inhibitor
1.0%
0.8920
100%
1.16
Final density
Test 4
This is compatibility test (this test is to certify the immiscibilty
between Solution [X] and reservoir fluid (crude)
Using our double ended cell, sample of refined mud filter cake
on a 40 micron aloxide disk is obtained via HTHP process. The
aloxide disk containing with the filter cake is immersed in the
soaking solution, and remove every 30mins/1hrs to evaluate the
rate of destruction
RESULT ANALYSIS
Phase stability
Approximately 400 ml of the final Solution [X] formulation
shall be transferred to a beaker and tested at 145˚F to check for
phase stability, for 24hrs. The samples should remain single
phase
Initial soaking blend
XXX
Equipment used in carrying out the experimental procedures
include,

A 4-scale metal mud balance

Retort kit

Rotational Viscometer

API Filter Press

Aloxide Disc

Roller oven

Heating Chamber

Back loaded mud samples

Pre mud samples/Freshly built mud
Soaking blend after 24 hour
EXPERIMENTAL PROCEDURE
Step 1. Mud property determination
Step 2. Scale formation and precipitation rate determination
The scale formation and precipitation for each mud type was
determined using the model as proposed by Fadairo et al (2008)
at varying temperature values
Step 3. Mud sample heated for varying time from 1hr to 14days
respectively
Step 4. Mud filtration rate determined for each sample
Step 5. Mud cake deposition on Aloxide disc
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
Test 1. This clean up test was carried out using freshly built mud (BLEND A)
The pictures below illustrate the filter cake destruction after exposing the filter cake/scale to Solution [X] for 8hrs 30mins.
174
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
There was a complete clean-up after 8hrs 30mins in the soak solution.
*We had a total break through time of 2hrs.
Test 2. This clean up test was carried out using back loaded mud (BLEND B)
The pictures below illustrate the filter cake destruction after exposing the filter cake to the new formulation for 10hrs.
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
176
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
There was a complete clean-up after 10hrs in the soak solution
* We had a total break through time of 2hrs 45mins
Test 3. This clean up test was carried out using Reconditioned mud (BLEND C)
There was a complete clean-up after 8hr 10mins in the soak solution
* We had a total break through time of 2hrs 05mins
Test 4. This is compatibility test (this test is to certify the immiscibilty between Solution [X] and reservoir fluid (crude)
1) Prepared 600mls each of Solution [X] using the following formulations as stated previously
2) Decanted 25%, 50% & 75% of respective crude samples into each labelled glass cylinders and filled up with Solution [X]
and shake sample.
3) Stood beakers upright and visually check for separation/precipitation/emulsion at room temperature (26 deg C) before
placing sample beakers into water baths to heat at 145˚f for 30mins.
Results:
Sample Description
Crude
Crude API / SG
31 / 0.87
Crude Grade
Light Oil
Temperature / Time
145˚F for 30mins
Emulsion Formation
No
Separation
Yes
Precipitation
No
TEST SAMPLE
A
B
Emulsion Formation
No
No
Separation
Yes
Yes
Precipitation
No
No
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 2 (2017) pp. 172-178
© Research India Publications. http://www.ripublication.com
Visuals:
CONCLUSION
A solution that reliably cleans the wellbore and unplugs
formation of BaSO4 scale formed either during or after a
drilling operation has been developed. Qualities of the solution
includes the following:
 The Solution [X] was able to clean up the filter formed
and render water wet the associated solids
 No visible phase separation was observed before and after
Solution [X] blend was heated for over 24 hours at
145degrees Fahrenheit in a water-bath. The sample passed
the test criteria maintaining a single phase.
REFERENCES
[1]
[2]
[3]
ACKNOWLEGDEMENT
The authors are grateful to Covenant University for the
financial support and permission to publish this work.
The study presented here has evolved from many discussions
with (DRILLING FLUIDS) specialist Mr. C. Eziokwubundu*
178
Pitzer, K. (1980). "Thermodynamics of Aqueous
Electrolytes Various Temperatures, Pressure and
Compositions". Thermodynamics of Aqueous Systems
with Industrial Applications, ACS symposium Series,
133, 393-414.
Fadairo, A. (2008). " Effect of oilfeild scale deposition
on Mobility ratio". CIPC/SPE Gas Technology
Symposium, (pp. SPE-114488). Calgary, Alberta,
Canada
Haarberg, T., I, S., Granbakken, D., Ostvold, T., Read,
P., & Schmidt, T. (1992). "Scale Formation in Reservoir
and Produstion Equptmentduring Oil Recovery II"
Equilibrium Model. SPE Journal Production
Equiptment, 7(1).